Science —

We don’t know much about the Atlantic Ocean currents

New research is showing that internal variability is dominating over expected …

The climate is an incredibly complicated system, which necessitates that scientists with a wide range of specialties cooperate to study it. So climatology has contributions from space science, hydrodynamics, paleosciences, and, among others, oceanography. It was discovered in the late 1980s that the oceans were actually a very important component of the Earth's climate, where small changes in ocean water temperatures could yield huge atmospheric weather changes. This also works in reverse, but the coupling is not nearly so strong—probably due to the higher heat capacity of water.

One of the changes that long-term atmospheric heating is expected to cause is a reduction of the speed of ocean currents. A particularly important ocean current is the Atlantic Ocean conveyor belt, which drives warm water along the northern European coast and keeps that area of the world considerably warmer. If this current were to stop, Europe would find itself in a spot of bother.

Given the importance of the Atlantic Ocean conveyor belt, it is quite crucial that we have extensive data on its flow—something that has been sorely lacking. We reported on the first results from a long-term study two years ago. This study used a string of buoys running along a constant meridian to send back a continuous stream of depth-dependent flow rates. The results didn't look good—the initial findings indicated a 30 percent slow down over 12 years. As noted by the researchers at the time, the data was noisy and that the slow down they measured could all be part of the current's internal variability.

This warning was borne out by follow up results that used new data from the buoy line and combined it with pre-existing data from other sources to get a picture of how the current... err... ebbed and flowed. Their conclusion was that all the data taken thus far fits within the bounds of natural variation.

Nevertheless, the data set is still quite sparse but the buoys are still out there. Now, in a paper to be published in <a href="http://www.sciencemag.org" title="Subscription required" <i="Science, the researchers have analyzed the 2004-2005 data set to estimate how long it will take to obtain enough data to be sure that the internal variability of the ocean current is properly bracketed. Their answer? Ten years.

This actually fits quite well with what we know about other aspects of climate research. We have been monitoring temperature, pressure, and precipitation with increasing accuracy for a long time. However, it is only in the last 100 years that we have begun to accumulate a continuous time series with any geographic resolution. From there, it has taken a good 40 years to pick out a statistically significant trend from the data. I guess you can look forward to ten more years of increasingly accurate Atlantic conveyor belt reports.

Science, 2007, DOI: 10.1126/science.1141304

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Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He Lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com//Twitter@exMamaku